Device for measuring pressure points to be applied by a compressive orthotic device

ABSTRACT

The device comprises a rigid former reproducing the volume of a portion of the body and suitable for receiving the compressive orthosis. The former ( 10 ) incorporates a plurality of sensors ( 22 ) distributed over various points of the former and configured in such a manner as to avoid significantly modifying the surface profile of the former, the sensors essentially measuring the pressure applied locally on the former by the orthosis at the location of the sensor and perpendicularly to the surface of the former. Advantageously, at the location of the measurement point, each sensor comprises a thin wall capable of being subjected to microdeformation under the effect of the pressure applied by the orthosis, and means such as a strain gauge bridge, for example. The thin wall can constitute a portion of a support pellet which is fitted to the former in such a manner that its outside surface, which includes the thin wall, is flush with the outside surface of the former.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to measuring the restraining pressures that acompressive orthosis serves to apply on a portion of the body.

2. Discussion of Prior Art

The invention is more particularly described for the case where theportion of the body in question is the leg and the compressive orthosisis an elastic stocking. Nevertheless, the invention is not limited tothat particular case and it applies to other types of orthosis and/or toother portions of the body, for example elastic strips for applicationto the leg or to a portion of the leg, a belt for applying pressure tothe abdomen, etc.

The pressures exerted by such orthoses are small, of the order of 0 to100 hPa, and typically of the order of 20 hPa to 70 hPa, in relativepressure terms.

Numerous factors can influence the value of this pressure and can giverise to differences from a standard nominal value, e.g. knitting machineadjustments, manufacturing tolerances, processing such as dying thestockings, etc.

It is therefore necessary to be able to measure accurately andreproducibly the pressure that is really applied by a given compressiveorthosis, in particular to verify that complies with nominal values(quality control during manufacture).

Until now, such measurement has been performed by placing the stockingthat is to be inspected on a wooden jig or “tree” of standardized shapeand dimensions (“Hohenstein model”, sizes 1, 2, 3, or 4), and by slidinga thin rubber capsule between the stocking and the tree, which capsuleconstitutes a pressure sensor (a device known as a “Compritest”), and bynoting the pressure given by the capsule, firstly without the stocking,and then with the stocking. The desired value is obtained by taking thedifference between those two values.

Nevertheless, that method suffers from three major drawbacks:

firstly, its accuracy is poor given that firstly the pressure applied bythe stocking is relatively small compared with the sensitivity of thepressure gauge capsule, and secondly because placing the sensor betweenthe stocking and the tree changes the tension of the stockingspecifically at the location where the measurement is being performed,thus falsifying the measurement;

measurement is difficult and highly dependent on the skill of theoperator since it is necessary to slide the capsule between the stockingand the tree while moving the stocking as little as possible: it is thusdifficult to ensure that the method is reproducible; and

finally, that method gives local measurements only and in order toobtain another measurement point it is necessary to repeat the operation(putting the capsule into place) as many times as there are desiredmeasurement points.

SUMMARY OF THE INVENTION

An object of the invention is to remedy those drawbacks, by proposing adevice that makes it possible to draw up a genuine map of the pressuresthat can be applied by a compressive orthosis on a portion of the body,and having the following advantages:

the measurement is accurate;

the measurement is faithful in that it provides data in a manner that isreproducible and independent of the skill of an operator;

measurements are performed on a large number of points simultaneously(or quasi-simultaneously if multiplexing is used, for example), therebyobtaining an anatomically representative grid for the map of pressuresapplied by the compressive orthosis;

it can be implemented simply and quickly; and

the various data measurements taken can be digitized, stored, processed,and displayed, in particular for the purpose of interfacing withcomputer processing.

To this end, the device of the invention which presents a rigid formerreproducing the volume of the portion of the body under investigationand suitable for receiving the compressive orthosis is characterized inthat the former incorporates a plurality of sensors distributed overdifferent points of the former and configured in such a manner as toavoid significantly modifying the surface profile thereof, and in thatsaid sensors essentially measure the pressure that is applied locally tothe former by the orthosis at the location of the sensor andperpendicularly to the surface of the former.

According to a certain number of advantageous features:

the sensors comprise, at each measurement point, a thin wall capable ofbeing subjected to microdeformation under the effect of the pressureapplied by the orthosis, and measurement means, in particular atemperature- compensated strain gauge bridge, for measuring saidmicrodeformation;

the thin wall forms a portion of a support pellet fitted to the formerin such a manner that its outside surface, which includes the thin wall,is flush with the surface of the former;

the device further comprises means for calibrating the sensors by meansof a leakproof enclosure that can be pressurized and that encloses theformer; and

the device further comprises means for processing and displaying themeasurements taken by the sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention is described below with reference to theaccompanying figures.

FIG. 1 is a diagrammatic partially-cutaway elevation view of the deviceof the invention connected to a computer for making use of the measureddata.

FIG. 2 is a view on a larger scale of the detail marked II in FIG. 1,showing the structure of one of the sensors of the device.

FIG. 3 is a section view on III—III of FIG. 2.

FIG. 4 is a block diagram showing the electronic circuits for processingthe measurement signals supplied by the sensors of the device of theinvention.

DETAILED DISCUSSION OF PREFERRED EMBODIMENTS

In FIG. 1, reference 10 designates overall a rigid former that isrepresentative of a limb (or more generally of a portion of the body) onwhich compression is to be applied. In the example shown, it isconstituted by a leg former having dimensions corresponding to one ofthe four sizes 1 to 4 of the standardized “Hohenstein model”.

The former 10 has a central core 12 or “salmon” made of metal having ahollow center so as to provide an access tunnel 14 serving specificallyto pass and keep together the wires connected to the various sensors(see below). The metal “salmon” 12 is covered in a covering 16, e.g. ofepoxy resin, that is molded to have the same dimensions as thestandardized jig or tree. The surface state of the covering 16 is madeto be smooth and without roughnesses so as to make it easy to put anelastic stocking into place in uniform manner on the former 10.

Advantageously, e.g. to make it possible to exchange a faulty sensor orto verify the interconnections, the former is made up of a plurality ofseparable elements that are assembled together in leakproof mannerwithout gaps, e.g. five independent elements respectively representing a“thigh”, a “knee”, a “calf”, an “ankle” and a “foot”.

The entire former is placed on a support ring 18 which is itself mountedon a box 20 that may, in particular, contain the electronics forprocessing the signals.

The former 10 is provided with a plurality of sensors 22 which aredescribed in greater detail with reference to FIGS. 2 and 3, the sensorsbeing placed at various successive levels up the leg, e.g. at sevensuccessive levels 24 to 36, with each level having five to elevensensors distributed around its periphery. The distribution of thesensors can be as indicated in the table below, giving a total of sixtysensors, i.e. sixty simultaneous pressure measurements at seven levelsalong the leg (with “height above ground” corresponding to the height ofthe sensor measured in the proximal direction from the sole of thefoot).

Height Angle Corresponding above No. of between linear Level groundsensors sensors spacing No. (cm) per level (°) (cm) 1 12 5 72 4.6 2 20 660 4.8 3 31 8 45 4.4 4 39 8 45 4.3 5 45 11 32.7 3.4 6 60 11 32.7 4.3 772 11 32.7 4.7

The assembly can be mounted on a rotary support 38 of the same type asthat used with traditional Hohenstein jigs to make it easy to put on thestocking.

The electronic unit 20 is connected by a link 40 to a microcomputer 42that performs signal processing and that displays the measuredpressures.

The structure of the sensors is described in greater detail withreference to FIGS. 2 and 3. FIG. 2 is a section in elevation through oneof the sensors 22, and FIG. 3 is a plan view, in section, through thesame sensor, showing the curvature of the leg.

The sensor 22 is made from a support pellet 44, e.g. made of epoxyresin, whose outside surface 46 is defined in such a manner as topresent locally the same curvature as the remainder of the leg and so asto ensure that there are no gaps relative to the outside surface 48thereof. Thus, the shape has no projections or discontinuities in thevicinity of a sensor, and therefore does not get in the way of puttingthe stocking on the former, and above all does not modify in any way theconditions under which pressure is applied to the leg by the stocking(unlike the prior art device in which a capsule is interposed betweenthe stocking and the jig, thereby locally modifying the conditions withwhich compression is applied).

Internally, the pellet 44 has a cavity 50 so as to define a thin wall ormembrane 52 between said cavity and the outside surface 46, which wallor membrane is capable of being subjected to microdeformation. The term“microdeformation” is used herein to mean a change of curvature that islarge enough to be measurable but small enough to avoid significantlymodifying on a macroscopic scale the local conditions with whichpressure is applied by the stocking to the measurement point.

Typical dimensions for a support pellet 44 are as follows: outsidediameter =24 mm; inside diameter of the cavity 50=13 mm; thickness ofthe diaphragm 52=0.75 mm; and radius of curvature of the surface 46=36mm to 80.5 mm depending on the location of the sensor. To measure themicrodeformation of the wall 52, a strain gauge 56 is stuck thereoninside the cavity 50, e.g. a bridge having four strain gauges of thekind that is suitable for measuring pressure by means of a diaphragm andthat is temperature compensated.

The power supply and measurement wires 58 of the strain gauge 56 passthrough the covering 16 and the metal “salmon” 12 via a strain gaugewell 54 that opens out into the access tunnel 14 and that enables thewires to be connected to a primary connector 60, itself connected to theelectronic unit 20 as are other corresponding connectors.

FIG. 4 shows the electronics circuits that enable measurement to beperformed: one of the diagonals of the strain gauge bridge 56 is fedwith two symmetrical voltages 62 and 64 while the other diagonal isconnected to two inputs of a differential amplifier 66, and the gain andthe offset of each amplifier can be adjusted individually by means ofrespective potentiometers 68 and 70. The output signal from theamplifier 66 is transmitted via a lowpass filter 72 to an analogmultiplexer 74 whose inputs receive the signals delivered by the variousamplifiers associated with the strain gauges of each of the sixtysensors in question. The output signal from the multiplexer 74 isapplied to the input of an analog card 76 of the microcomputer 42 whichaddresses the multiplexer 74 via a bus 78 so as to cause it to supply aline 80 with one of the sixty measurement signals coming from thesensors.

The sensors are scanned cyclically and continuously, thereby making itpossible simultaneously to provide a varying display of all of thepressure values observed at the various measurement points.

These values can be displayed in digital form (value of the relativepressure in hPa), and also in graphical form, e.g. using a bar chartand/or a colored graphic, where color varies relative to the referencepressure for the measurement point under consideration (e.g. green ifthe pressure differs by no more than a predetermined amount from thereference value, and red otherwise).

The measured values can also be subjected to various mathematicalprocesses, for example a mathematical model can be applied in whichparameter values are determined for each measurement point for thepurpose of compensating local effects such as the thicknesses of thesensitive walls which depend on the radius of curvature of the former atthe corresponding location.

In order to adjust the individual gain and offset parameters for each ofthe amplifiers 66, an initial step is provided in which the sensors arecalibrated, which step is performed by putting the entire device in anenclosure 82 (FIG. 1) and then putting said enclosure under accuratelycalibrated pressure: adjustments are then performed until all of thesensors display the same pressure value: zero pressure when theenclosure 82 is absent, and calibration pressure after the enclosure 82has been pressurized.

This adjustment can be performed in various ways: the gain and offsetpotentiometers can be adjusted manually, the gains and the offsets canbe adjusted under program control from the microcomputer, or indeed bychoosing amplifiers that avoid the need for compensation.

The invention has numerous applications, amongst which the following canbe mentioned:

in a factory, adjusting knitting machines and performing productionquality control;

in a clinic, as an analysis tool for verifying that the compressionactually applied by the orthosis confirms with the compressionprescribed by the practitioner, or for dynamically studying pressurevariations as a function of movements of the limb (in which case theformer needs to be jointed);

in the field of teaching for training in the technique of puttingcompression strips into place: by displaying pressures immediately, itis possible immediately while the strip is being put into place to seewhether the tension of the strip is too little or too much; and

in the military field for evaluating the effectiveness of “anti-g” suitswhich apply pressures in controlled manner to certain portions of thebodies of fighter pilots in order to compensate for the highaccelerations to which they can be subjected in flight.

What is claimed is:
 1. A device for establishing a simultaneous map ofpressures applied by a compressive orthosis on a portion of the body,said device comprising: a rigid former reproducing the volume of saidbody portion and suitable for receiving the compressive orthosis, aplurality of embedded sensors (22) distributed over different points ofthe former and configured in such a manner as to avoid significantlymodifying the surface profile thereof, said sensors essentially measurethe pressure that is applied locally to the former by the orthosis atthe location of the sensor and perpendicularly to the surface of theformer.
 2. The device of claim 1, in which the sensors comprise, at eachmeasurement point, a thin wall (52) capable of being subjected tomicrodeformation under the effect of the pressure applied by theorthosis, and means for measuring said microdeformation.
 3. The deviceof claim 2, in which the means for measuring the microdeformation of thethin wall comprise a temperature-compensated strain gauge bridge (56).4. The device of claim 2, in which the thin wall forms a portion of asupport pellet (44) fitted to the former in such a manner that itsoutside surface (46), which includes the thin wall, is flush with thesurface (48) of the former.
 5. The device of claim 2, further comprisingmeans for calibrating the sensors by means of a leakproof enclosure (82)capable of being pressurized and that encloses the former.
 6. The deviceof claim 1, further comprising means (20, 42) for processing anddisplaying the measurements taken by the sensors.